Planar optical scanning head having deficiency-correcting grating

Abstract

A planar optical head is described with a corrected input grating for scanning a surface, for example, a recording surface (2) in an optical record carrier (1). A radiation source (5) supplies a beam (6) which is coupled into a waveguide (9) by an input grating (7) and is formed to a focused scanning beam (11) by an output grating (10). Deficiencies of the radiation beam such as the non-round cross-section of the beam, astigmatism and wavelength variations caused by the radiation source can be corrected by means of an adapted grating structure of the input grating.

I claim: 
     
       1. An optical head for scanning a surface, which head is provided with a source supplying a radiation beam, an input grating having a periodic grating structure for coupling the radiation beam as a deflected beam into a waveguide, and an output grating for coupling radiation out of the waveguide and for directing said radiation in the form of a scanning beam onto the surface, characterized in that the input grating is configured to provide at least one correction for a deficiency of the radiation beam. 
     
     
       2. An optical head as claimed in claim 1, characterized in that the input grating and the output grating are configured to provide a correction for wavelength variations of the radiation beam, in which the input grating and the output grating are each divided into n groups of m identical sectors which are associated with each other and are located symmetrically with respect to each other, in which the corresponding groups of sectors of the two gratings form part of a radiation path for a beam having a given wavelength of the radiation source, and in which n and m are integers which are larger than one. 
     
     
       3. An optical head as claimed in claim 2, characterized in that a lens is arranged in the optical path of the scanning beam. 
     
     
       4. An optical head as claimed in claim 1, characterized in that a lens is arranged in the optical path of the scanning beam. 
     
     
       5. An optical head for scanning a surface, comprising means for providing a radiation beam, a waveguide, an input grating having a periodic structure for coupling said radiation beam into said waveguide, and an output grating fro coupling radiation out of the waveguide and for directing said radiation as a scanning beam toward said surface, characterized in that said grating structure deviates from a completely symmetrical circular grating structure, the deviation from complete circular symmetry correcting at least one deficiency of said radiation beam.   
     
     
       6. An optical head as claimed in claim 5, characterized in that a lens is arranged in the optical path of the scanning beam. 
     
     
       7. An optical head as claimed in claim 5, characterized in that the input grating and the output grating are configured to provide a correction for wavelength variations of the radiation beam, in which the input grating and the output grating are each divided into n groups of m identical sectors which are associated with each other and are located symmetrically with respect to each other, in which the correponding groups of sectors of the two gratings form part of a radiation path for a beam having a given wavelength of the radiation source, and in which n and m are integers which are larger than one. 
     
     
       8. An optical head as claimed in claim 7, characterized in that a lens is arranged in the optical path of the scanning beam. 
     
     
       9. An optical head as claimed in claim 5, characterized in that the input grating has a correction for astigmatism of the radiation beam in that the periodic grating structure comprises non-circular grating lines in which the grating period is different in two directions which are perpendicular to each other. 
     
     
       10. An optical head as claimed in claim 9, characterized in that a lens is arranged in the optical path of the scanning beam. 
     
     
       11. An optical head as claimed in claim 9, characterized in that the input grating and the output grating are configured to a correction for wavelength variations of the radiation beam, in which the input grating and the output grating are each divided into n groups of m identical sectors which are associated with each other and are located symmetrically with respect to each other, in which the corresponding groups of sectors of the two gratings form part of a radiation path for a beam having a given wavelength of the radiation source, and in which n and m are integers which are large than one. 
     
     
       12. An optical head as claimed in claim 11, characterized in that a lens is arranged in the optical path of the scanning beam. 
     
     
       13. An optical head as claimed in claim 12, characterized in that a lens is arranged in the optical path of the scanning beam. 
     
     
       14. A head as claimed in claim 5, characterized in that said input grating structure comprises non-circular grating lines having a grating period different in two directions which are perpendicular to each other. 
     
     
       15. A head as claimed in claim 5, wherein said radiation beam has a non-circular cross-section, characterized in that said input grating structure covers a surface having the size of said cross-section at the location of the input grating. 
     
     
       16. An optical head as claimed in claim 15, characterized in that the input grating and the output grating are configured to provide a correction for wavelength variations of the radiation beam, in which the input grating and the output grating are each divided into n groups of m identical sectors which are associated with each other and are located symmetrically with respect to each other, in which the corresponding groups of sectors of the two gratings form part of a radiation path for a beam having a given wavelength of the radiation source, and in which n and m are integers which are larger than one. 
     
     
       17. An optical head as claimed in claim 16, characterized in that a lens is arranged in the optical path of the scanning beam.